Normal BG level during exercise (high range is?)

I know my BG spike 1 or 2 mmol/l from 5.5-6.2(before sport) during exercise. Today I was surprised to find I had 2 spikes (one 8.9 and another 8.2) at the game. Because today (badminton game) is quite a close match and we played quite seriously (each is 30 minutes), after game I see the spike and then I sit and wait for 45 minutes to see it drop back to 6.2 as fast as it rised to 8.x

So my questions is
1. What's the "concernable" spike reading during the exercise?
2. What's the solution to avoid it, if >8 spike is bad thing? Option 1: NO game. 2.Take a break during game; 3. Reduce the game length and get full break between games 4. Finish all games (let the BG keeping peak level other than up and down.) then go home. 5. Open to suggest

Sorry I started a new thread since it is not very clear what we are discussing now on the "Normal Sugar Level" thread.